The overall objective of this research programme is to probe the structure and function of microtubules and membranes in normal, pathological and drug-treated cells. The drugs of particular interest are two carbamate herbicides IPC and CIPC that disrupt the mitotic apparatus of plant cells. These herbicides appear to similarly inhibit mitosis in 3T3 fibroblasts. However, they do not inhibit colchicine binding activity or polymerization of purified tubulin. Their effects on fibroblast mitosis persist after withdrawal of drug and reinitiation of cell division. Current aims are to quantify mitotic inhibition, confirm delayed recovery of mitotic spindle assembly and find out if microfilament disruption represents a primary site of drug action. Other studies will explore the normal regulation of microtubule assembly and interactions between microtubules and microfilaments. These results will be applied to the analysis of herbicide action.